I mean, how for example article will be posted exactly in 16:00?
There is a cron that checking the schedule posts every minute?
I’m asking because i want to write crawler, that will bring content from specific website each time that this website will post a new content.
The same example we see in Google reader, each new article from your subscribed websites, reader will show right away
Thanks!
When a user visits the site (any user), a pseudo-cron job runs. Basically, every PHP page is hooked up to a cron-like environment that executes code when called.
I say “pseudo” because you can’t distinguish it from a real one. The only way you can tell would be to browse the webpage to check for new content, triggering the job (which happens as you request the page).
As for the crawler, why do you need to crawl it? Just download the RSS feed (most themes support it). It contains all of the recent posts in a nice format.
As @Blender noted, the events are triggered by a psuedo-cron process which runs when a user accesses the home page. It will execute scheduled actions as long as their scheduled time has passed.
You can hook your own behaviors into this process. See these pages on the WordPress Codex around WP-Cron, specifically this one about scheduling events.